In the treatment of various illnesses and diseases, many different types of solutions or medicaments are injected into the veins of patients. Many devices are provided in the prior art for handling such solutions and medicaments and for injecting the solutions and medicaments into the veins of a patient. During the preparation, handling and injection of such solutions and medicaments into the veins of a patient, contaminants are frequently introduced into the solutions or medicaments. Some examples of contaminants are small pieces or particles of flash which break off of the injection apparatus, or pieces of stoppers or vials or cartridges which are punctured or broken in the preparation of a solution or medicament for injection into the vein of a patient. These contaminants must be removed prior to injection of the solutions or medicaments into the veins of a patient, and various filtration devices are known in the prior art for removing these contaminants. For example, specially shaped screen type filter discs have been employed in the prior art to obtain maximum filtration area, but such screen type filter discs are relatively expensive to make and are difficult to assemble. Further, it is difficult to place such filter discs in intravenous apparatus in such a manner that the construction is leakproof, with all flow occurring through the filter disc. In some instances with prior art filters, the solution or medicament seeps around the filter disc and thus all of the contaminants in the solution or medicament are not removed.
Another filter used in the prior art is commonly referred to as a depth filter. A depth filter consists of fibers, particles or fragments of materials of some type pressed or bonded together to form a tortuous maze or flow passage. The pores of a depth filter can be made course or fine or variable in size. Initially, such filters have a high flow rate and contaminants are entrapped throughout the matrix of the filter, with contaminate particles working their way through the filter until they are trapped therein. Such filters are highly susceptible to clogging with a resultant increase in the operating pressure or pressure differential thereacross and some of the contaminants may eventually work their way through the filter.
With the present invention, a simple and unique construction is provided wherein a screen type filter disc is sealed to an insert and the insert and filter are then positioned within a needle adapter across a bore therethrough to filter contaminants from a solution or medicament passed through the adapter. The filter disc according to the present invention is sealed to the insert so that there is no possibility of the solution or medicament leaking or seeping around the filter. In a preferred form of the invention, the filter is dome shaped, with the dome shape being automatically achieved when the filter is secured to the insert; and accordingly, the filter disc of the present invention is substantially more economical, is easier to assemble, and is more efficient than prior art filters.
Still further, it is difficult to achieve a constant flow rate in conventional IV sets as the source of liquid to which the IV set is connected becomes depleted. For example, when an IV set is connected to a bag containing a liquid to be administered to a patient or to be mixed with another material or the like, the initial pressure, and thus the flow rate through the device is relatively high due to the available head pressure of the liquid. However, as the liquid in the bag is depleted, the head pressure is reduced and thus the flow rate decreases. The change in flow rate or drip rate (drops per minute) from initial flow to final flow in such a system can typically vary approximately 771 percent over a three hour period. A change in drip rate or flow rate of this magnitude is clearly critical and some means of controlling the rate must be provided. In the prior art, various devices, such as clamps and the like, are used to regulate the flow rate, but such devices require constant attention and frequent adjustment to insure that the proper flow rate is obtained, thus requiring the attention of a nurse or other person.
The present invention provides at least a pair of filters in the IV set, with the filters serially arranged, preferably one at or near the inlet end of a length of IV tubing, as for example, near or in a drip chamber, and another at or near the outlet end of the length of tubing, as for example in a filter adapter and needle assembly. The pair of filters thus provided, surprisingly results in a nearly constant flow rate through the IV set during the time it takes to deplete the liquid in the bag.